# std::flat_multimap<Key,T,Compare,KeyContainer,MappedContainer>::keys

From cppreference.com
< cpp‎ | container‎ | flat multimap

const key_container_type& keys() const noexcept; |  | (since C++23)

Return a constant reference to the adapted keys container. Equivalent to return c.keys;.

### Parameters

(none)

### Return value

The underlying keys container.

### Complexity

Constant.

### Example

Run this code

    #include <flat_map>
    #include <print>
    #include <type_traits>
    #include <vector>

    int main()
    {
        std::flat_multimap<int, double> adaptor{{1, 1.1}, {2, 2.2}, {3, 3.3}};

        // The default keys container is std::vector:
        static_assert(std::is_same_v<decltype(adaptor.keys()), const std::vector<int>&>);

        std::println("{}", adaptor.keys());
    }

Output:

    [1, 2, 3]

### See also

values | direct access to the underlying values container (public member function)

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